When Mariners general manager Jerry Dipoto swung a July 31 deadline deal with Baltimore, the low-key trade was seen strictly as a salary dump.

Wade Miley was costing $6.1 million to be a not especially effective No. 5 starter in 2016, and receiving anything more than a bag of sand in exchange for the veteran lefty would be a bonus.

Turns out the guy Dipoto got for Miley has been the team’s ace in the playoff race. Ariel Miranda on Sunday won for the fourth time in four September starts. The rookie’s seven-inning effort in a 7-3, stop-the-bleeding victory over Houston allowed the Mariners to cut Toronto’s lead for the second wild-card berth to two games.

Miranda was a pillar of poise in what could be described as the most significant game of the season at Safeco Field — until Monday night, that is, when the Blue Jays visit.

Never miss a local story.

Sign up today for unlimited digital access to our website, apps, the digital newspaper and more.

“I don’t think he thinks about the pennant race,” manager Scott Servais said of the 27-year old left-hander. “I think he’s trying to figure out a way to be part of this team and try to be comfortable and do what he needs to do in order to create a future for himself.

“Along the way, we’re benefiting.”

Miranda certainly figured out Houston, a team of free-swingers that leads the American League in strikeouts. Miranda fanned eight while allowing a pair of bases-empty homers, enticing the Astros with a fastball that had what Servais called “late life up in the zone.”

Up in the zone can be dangerous for a pitcher to work, but going there every so often can be an effective way of enticing pop ups and warning-track flies.

“He’s a fly-ball pitcher, that’s just who he is,” Servais continued. “Attacking the zone and getting hitters in a swing mode has been key for him.”

Before he showed up this summer, there wasn’t much of a book on Miranda. A native of Havana, he was signed to the minor leagues by the Orioles a year ago this past May, and didn’t make his first major-league start until Aug 4 with the Mariners.

Miranda began September with a 1-1 record, a 4.98 ERA with the Mariners, and the apparent future of a long-relieving/spot-starting journeyman destined to bounce between Triple A and the bigs.

Then he went six innings to earn a victory over the Angels on Sept. 2, six innings to beat the Rangers on Sept. 7, and six innings for another victory over the Angels on Sept. 12.

Along the way, he put together a streak of 19 consecutive innings without allowing an earned run, fifth longest for a Mariners rookie.

“His first couple of outings, he was trying to be too fine,” said catcher Mike Zunino. “He’s not that type of pitcher. He’s got to trust his stuff in the zone and let guys be aggressive on him.

“He’s sort of learning who he is.”

As are we. Before defecting from Cuba by way of Haiti (where he established residence) and the Dominican Republic (where he trained), Miranda pitched for seven seasons in the Cuban National Series, which he joined at the age of 17.

Listed at 6-foot-3 and 168 pounds, Miranda’s fastball tops out at around 91 mph. It’s not an unusually impressive pitch, but sets up a change up that is.

Miranda’s ability to remain unfazed in high-pressure games seems to be steeped in the resolve required to escape one country and make a new home in another.

“You can’t be afraid of something you enjoy doing,” he said through an interpreter Sunday, adding that pitching in a playoff game “is something I’ve never had the opportunity to do. It would be great for the people to get there.”

Concluded Servais: “You can see his confidence growing and it’s fun to watch. He believes in himself, and that’s half the battle at this level.

“You have to believe you belong and can be a contributor on a winning team.”

As Miranda continues to learn who he is, the Mariners keep on keeping on. Their most consistent starter at crunch time has turned out to be a pitcher who wasn’t on anybody’s radar screen two months ago.

Quite a haul for the trade that wasn’t supposed to bring back more than a bag of sand.